Into a 0.68-inch high enclosure, Apple has dropped a modern high-performance engine where an old poky one used to be. That new powerplant would be Intel's newest power-efficient Core i5 processors, of course.

2011 MacBook Air.Photo by CNET Reviews

Where a Core 2 Duo--introduced way back in 2006--was, the new MBAs house spanking new Sandy Bridge chips. Intel's newest design is two generations removed from the Core 2 Duo. And that means you get nice design extras like processors that overclock automatically when applications demand bursts of speed. Intel calls this turbo frequency.

So what's under the hood specifically? The i5-2467M (11.6-inch model) and i5-2557M (13.3-inch) processors, running at 1.6GHz (with turbo speeds up to 2.3 GHz) and 1.7GHz (can turbo up to 2.7 GHz) respectively.

There is also an option for an 1.8GHz Core i7 (add $100), which by all appearances is an i7-2677M that turbos to 2.9GHz. The i7 has a slightly larger cache, 4MB versus 3MB for the i5s. A larger cache typically means better performance.

And these processors deliver on performance--in tandem with fast solid-state drives. CNET Reviews' Dan Ackerman has run some initial tests (below) that are indeed impressive. (Also see CNET Reviews' product pages here and here.) The Multimedia Multitasking and Adobe Photoshop CS3 show impressive gains for both 2011 MBA models. And Apple iTunes encoding results show that we're talking about more than a small performance uptick.

The i5s and i7 used in the ultra-skinny Air are not gas-guzzlers. They're Intel's most power-efficient i series chips--what Intel used to refer to as ULV or ultra-low-voltage. All are rated at a cool 17 watts, rather the 25 or 35 watts for mainstream Intel laptop processors.

And for those willing to crack open an Air, the solid-state drive (ranging up to 256GB) is not soldered on the logic board, iFixit said. So it's user upgradable. That said, you're out of luck if you need extra RAM.

Apple MacBook Air Summer 2011 performance charts: initial benchmark scores. (Note: A full review with complete benchmarking and battery life scores will come later at CNET Reviews.)